It is well known that as the expansion ratio of an internal combustion engine is increased, more energy is extracted from the combustion gases and the thermodynamic efficiency increases. However, conventional spark ignited internal combustion engines usually have substantially the same compression and expansion ratios, the maximum value of both being determined by the selected compression ratio at full throttle which is preferably just below the point of combustion detonation. Typically, combustion detonation usually occurs at compression ratios ranging from 8 and 12-to-1 depending upon the combustion chamber design, operating conditions and the anti-knock characteristics of the fuel. Equal compression and expansion ratios are desirable at full throttle because the greatest torque output is produced. Under partial load conditions, however, the cylinder pressure-temperature conditions at ignition are well below those that produce detonation, particularly under very low load demand conditions. It is therefore desirable to increase the pressure-temperature levels at part load, an objective achievable by variably reducing the cylinder clearance volume as the charge is decreased in such manner that the compression pressure and temperature parameters remain essentially constant at a level below detonation at all levels. This permits the greatest possible expansion of the combustion gases to take place and consequently provides the highest possible thermodynamic efficiency. In internal combustion engines used to power vehicles wherein a wide range of engine speed and power outputs are essential, a throttle-equipped carburetor is customarily utilized. The carburetor throttle valve controls the charge quantity by restricting the flow to the intake manifold, thereby creating a partial vacuum which limits the charge mass inducted during each piston constant displacement intake stroke. It is well known that throttling the charge involves unavoidable induction pumping work with attendant loss in engine brake efficiency.
Prior art teachings include various proposals for spark ignited internal combustion engines in which the charge mass and clearance volume are varied in unison in accordance with load demand. For example, attempts have been made to maintain the compression pressure nearly constant at all load levels by varying the clearance volume in proportion to manifold pressure. Other designers propose variably delaying closure of the intake valve at or beyond the bottom of the intake stroke to control the charge quantity without need for a throttle valve, the objective being to avoid pumping losses and work to induct the entering charge, but this necessitates making some provision for beneficial utilization of portions of the charge not needed for induction under less than full load conditions. In general, practical considerations necessitate restricting such arrangements to four stroke engines employing four cylinders, or multiples thereof, wherein the intake strokes are symmetrically timed with respect to crank-shaft rotation angle and so designed as to prevent carburetor back flow pressure surges. It has also been proposed to variably advance the closure of the intake valve as it approaches bottom dead center in an effort to control the inducted charge without need for a throttle valve.
It is evident that these prior proposals are subject to certain serious disadvantages and shortcomings avoided by this invention. For example, these prior teachings involve complex constructions which are costly to manufacture, service and maintain. Additionally, many lack feasible and suitable load responsive control means. A further and particularly serious shortcoming of all is the lack of means for avoiding engine pumping looses at less than full load. Illustrative of the state of the prior art depicting these shortcomings are the following U.S. Pat. Nos.: Higginbottom, et al. 887,633; Mono 1,160,970; Salisbury 1,219,781; Spohrer 1,361,110; Halton 1,404,366; Wood 1,539,227; Woolson 1,794,047; Talbot 1,812,572; Cook 2,062,209, Andrean 2,120,012; Hironaka 2,153,691; Aspen 2,387,973; Woodruff 2,433,639; Hickey 2,500,823; Ericson 2,523,105; Pettit 2,589,958; Hickey 2,647,498; Ericson 2,770,224, Biermann 2,873,728; Huber 3,633,552; and Wilson Re. No. 18,595.